Seasonality is an important aspect associated with population dynamic and structure of tropical insect assemblages. This study evaluated the effects of seasonality on abundance, richness, diversity and composition of an insect group, drosophilids, including species native to the Neotropical region and exotic ones. Three preserved fragments of the northern Atlantic Forest were surveyed, where temperatures are above 20 °C throughout the year and rainfall regimes define two seasons (dry and rainy). As opposed to other studies about arthropods in tropical regions, we observed that abundance of drosophilids was significantly higher in the dry season, possibly due to biological aspects and the colonization strategy adopted by the exotic species in these environments. Contrarily to abundance, we did not observe a seasonal pattern for richness. As for other parts of the Atlantic Forest, the most representative Neotropical species (Drosophila willistoni, D. sturtevanti, D. paulistorum and D. prosaltans) were significantly more abundant in the rainy season. Among the most abundant exotic species, D. malerkotliana, Zaprionus indianus and Scaptodrosophila latifasciaeformis were more importantly represented the dry season, while D. simulans was more abundant in the rainy period. The seasonality patterns exhibited by the most abundant species were compared to findings published in other studies. Our results indicate that exotic species were significantly more abundant in the dry season, while native ones exhibited an opposite pattern.

Host specialization to form biotypes is common among phytophagous insects, and it has been hypothesised that biotypes of Dactylopius tomentosus L. (Hemiptera: Dactylopiidae) occur. D. tomentosus is an important biological control agent for Cylindropuntia cacti when they occur as weeds. Additionally, there is uncertainty surrounding the taxonomic status of some species of Cylindropuntia. This study aimed to confirm the existence of D. tomentosus biotypes and to assess whether host specialization can help to resolve this systematic uncertainty. For this study, the host specificity and performance of ten provenances of D. tomentosus collected from C. cholla, C. fulgida var. fulgida, C. imbricata, C. f. var. mamillata, C. rosea and C. tunicata and reared on C. cholla, C. fulgida var. fulgida, C. imbricata and C. rosea were investigated. Five life-history parameters were measured including: crawler development time and survival, female development time, and the weight and number of eggs produced by females. Results revealed significant variation in host specificity with provenances either thriving, surviving or dying on the different hosts, thus demonstrating the existence of biotypes. Also, host specificity was related to host species and not to the geographic locality from which either the host or provenance was sourced. These findings suggest that the characteristics of Cylindropuntia species may differ sufficiently, there by presenting different selection pressures that induce and sustain distinct biotypes of D. tomentosus. The observed host use patterns of the biotypes separated the plant species into two groups that accorded with known phylogenetic relationships among Cylindropuntia species, suggesting that biotypes can be used to elucidate their taxonomic relatedness. Besides advancing our knowledge of the ecology and evolution of D. tomentosus, these novel findings have important implications for the biological control of Cylindropuntia species.

The object of the present work is to study the histological picture of the intestinal tube of insects when subjected to the action of insecticides, in order to discover the mechanism of the action of poisons on insects.

Host-feeding by parasitoid wasps has been viewed as a positive attribute for biological control, because hosts are killed as a result of host-feeding in addition to parasitism. Host acceptance and host-feeding responses o unparasitized vs. conspecifically parasitized hosts by the parasitoid wasp Itoplectis naranyae Ashmead were studied in the laboratory. Female I. naranyae selected to oviposit in unparasitized hosts and those that had been parasitized I h previously, in equal proportions, even when allowed access to both types of host. Females also fed upon both types of host equally. Females, however, avoided ovipositing in hosts parasitized 40 h and 70 h previously, and preferentially fed upon them when allowed access both to parasitized and to unparasitized hosts. Parasitoid progeny in hosts which had been used for host-feeding suffered a high degree of mortality. Females used host internal changes as cues for deciding whether to feed on hosts. It is suggested that immature parasitoid mortality can be increased due to female preference for using parasitized hosts for host-feeding. Hence, host-feeding by I. naranyae may not be an advantageous biological control characteristic. The adaptive significance of selective host-feeding is also discussed.

The blood feeding patterns of Anopheles freeborni Aitken and Culex tarsalis Coquillett were studied, and the effects of host availability on these patterns were assessed in four different habitats within a northern California rice agroecosystem. Resting mosquitoes were collected from June to September of 1991 and 1992. The source of mosquito blood meals was identified with the modified precipitin test. Anopheles freeborni exhibited a ‘specialized’ (fixed) blood feeding pattern, predominantly (99% of the time) feeding on mammalian hosts; leporids and bovids were the major hosts, while equines, suids, and other mammals were minor hosts. Culex tarsalis exhibited a more ‘generalized’ (catholic) blood feeding pattern, taking blood meals from both birds and mammals at a ratio of 3:1 with Passeriformes being the most fed upon host group. Human blood indices were under 3% for both mosquito species, and multiple blood meals were estimated at less than 2%. The host feeding patterns for both mosquito species differed among the four (riparian, rice, pasture and mixed) habitats. The host feeding pattern for C. tarsalis reflected the distribution of both mammalian and avian hosts available. On the contrary, the host feeding patterns for A. freeborni reflected the distribution of mammalian but not the available avian hosts. Overall, host availability may be an important determinant of population size of some mosquito taxa (e.g. A. freeborni) than others (e.g. C. tarsalis) in rice culture agroecosystems.

Methods have been devised and applied to an intensive study of the course of illworm activity on numerous rain-grown and irrigated crops. These were developed the first instance to enable accumulation of data considered essential for evaluating eusefulness of certain egg and larval parasites when released experimentally. and they have now been extended to the point of providing continuous, quantitative data on bollworm-food-plant relations. This work has been placed on a routine basis. The information that is supplied comprises:—

1. The course of oviposition in point of duration, magnitude and time of occurrence in the life of a host crop. This serves well to indicate the true course of moth activity on different food-plants, the relative attractiveness of these and to reveal if such matters are maintained under different conditions and bear definable relations to growth stages of a food-plant.

2. The identity and activity of egg and larval parasites under natural conditions.

3. The identity and activity of insects predatory on the eggs and larvae, as occurring in the varied insect communities associated with different crops.

4. Comparative mortality of larvae in the different crops where oviposition has been recorded.

Continuous records of egg-laying by the American bollworm, H. obsoleta, F., have been taken at the Cotton Station, Barberton and on several farms in the neighbourhood. Cotton and maize were the principal crops, but the surveys included a number of other food-plants. Egg-laying was found to be very closely associated with the period of bud and flower production, and its duration on different hosts thus varies according to the flowering habit.

In the case of maize, egg-laying hi quantity commences when the tassels (stam-inate flowers) are extruding, and the peak of the oviposition is passed before silks (pistillate flowers) are abundant. This is at variance with the generally accepted view that the plant is most heavily oviposited upon during the silking period. The typical course of oviposition on maize here lasts for two to three weeks only.

Numerous instances were observed where oviposition by Heliothis occurred on maize in tassel to the practical exclusion of neighbouring cotton in freely fruiting and healthy condition, and the possibilities of exploiting this relationship are discussed.

As regards winter-irrigated vegetable crops and citrus orchards, data are given showing that the American Bollworm breeds extensively in these crops, particularly so a month or two prior to the appearance of rain-grown cotton, maize and tobacco.

The irrigated crops in the Barberton and contiguous districts are regarded as a main source from whence bollworm on cotton is derived. Citrus orchards of which there are relatively large acreages may be of particular importance in this regard.

The methods of obtaining information on the course of moth emergence are described. Data are given that explain the course of moth activity in winter crops and indicate when moths enter rain crops from winter breeding areas.

The only larval parasite of importance under natural conditions is Sturmia inconspicua, but this fly does not parasitise young larvae. There is a scarcity of insects parasitic on American bollworm larvae, and the question of importing them should be considered. Breeding and experimental releases of a larval parasite, Microbracon brevicornis, are discussed.

Two important egg parasites are a species of Phanurus and Trichogramma lutea.

An Anthocorid bug, Orius sp., destroys large numbers of bollworm eggs and probably also young larvae, and this insect and certain species of ants are the most important agents in natural control.

As regards the red bollworm, Diparopsis castanea, Hmps., it is concluded that the use of trap crops should be discouraged for general adoption as a means of controlling it owing to the danger, through inattention to the trap crops, of breeding this boll-worm in them. Its incidence in former years is briefly reviewed. Of late years the annual infestation has diminished greatly in some districts but not in others. The variations in this regard are attributed mainly to the presence or otherwise of ratooned cotton, particularly in mild winters and to seasons of very late planting.

The host range and feeding habits of seven species of Culex mosquitoes at Keneba, the Gambia, are described from precipitin tests of blood-meals and from observations on their attraction to calf, man, duck and pigeon baits. Feeding habits were classed nonspecific, mammalian or ornithophilic. Culex thalassius Theo. was non-specific, bloodmeals being identified from mammals (59·5%), birds (38·1%) and reptiles (2·4%). Large numbers were attracted to calf, man, ducks and pigeons. C. tritaeniorhynchus Giles fed almost exclusively on cattle: 17 of 19 blood-meals were identified as from cow. Many specimens were taken at calf, smaller numbers at man, and the few attracted to ducks fed readily. Birds were the main source of blood for C. decens Theo. (54·8%), C. invidiosus Theo. (87·5%), C. nebulosus Theo./cinereus Theo. (93·3%), C. tigripes Grp. & Charm. (98·3%), C. univittatus Theo. (two out of three) and C. weschei Edw. (one out of one). Reptile feeds were recorded for C. decens (14·3%), C. invidiosus (5·0%), C. nebulosus/cinereus (6·7%) and C. univittatus (one out of three). C. invidiosus and C. univittatus were common only at pigeon bait where some 13% fed on the birds.

Survivorship curves for the pre-adult stages of Pieris rapae (L.) on kale in Massachusetts exhibited two patterns. Early season generations showed a linear decline with mortality in all stages, whereas late season generations showed reduced losses in larval instars 2-4 and a concentration of mortality in the fifth instar. Ratios of direct measurement of recruitment of P. rapae and its parasitoid Apanteles glomeratus (L.) to their first larval and egg-plus-larval stages, respectively, indicated that losses to parasitism for five host generations were 86·1, 9·1, 58·O, 71·7 and 40·3% for the 1985 third generation and the 1986 first to fourth generations. Patterns of percentage parasitism within single generations were determined by higher rates of mortality in parasitized than healthy older larvae (instars 3-5) and, in some cases, by higher rates of host than parasitoid recruitment towards the end of the generation.

Our knowledge of the distribution of tsetse-flies affecting domestic stock in Kenya Colony is of a very general character. A good deal of the information requires confirmation; and much needs to be done to ascertain the extent and the nature of the permanent fly-infested areas, and the seasonal dispersion of the tsetses from their permanent haunts.

The demographic performance of a laboratory strain of Phthorimaea operculella (Zell.) was characterised by measurements of seven parameters under standard breeding conditions at six constant temperatures. The parameters were fertility, larval survival, sex ratio, weight of females, fecundity, development time and adult life-span. This information provides reference values which would be useful in experiments designed to determine the demographic effects of treatments, to identify strains and genetic populations of the species, and eventually to detect evolutionary changes in the specific properties of forms under study. The results of this investigation could be used in constructing simulation models of the species’ life system.

A previous study on the population dynamics of the cassava mealybug, Phenacoccus manihoti (Matile-Ferrero), on cassava has shown that populations increase during the dry season. The aim of the present studies was to determine whether these important changes in the pest population observed throughout the seasons in the field in the Congo, could be correlated with seasonal variations in the level of secondary compounds in the phloem, implicated in cassava plant resistance to P. manihoti. Our results showed that cassava was in drought stress conditions during the dry season (foliar area decreased). The combination of infestation and dry stress factors was clearly visible during the dry season. In fact, the decrease in leaf water potential together with infestation by P. manihoti was clearly observed at the end of the rainy season and during the dry season. The levels of the secondary compounds, rutin (an unfavourable substance to P. manihoti) decreased in the less resistant genotype, and cyanide (a phagostimulant substance) increased in each genotype in the dry season. These results may partially explain the important population changes in P. manihoti during the seasons.

The ovipositional behaviour of the mirid predator Macrolophus caliginosus Wagner, a potential biological control agent of glasshouse pests, was studied in detail using a modified video camera technique. In the laboratory, females laid their eggs in the leaves of tobacco plants. They remained generally motionless on the main veins of the leaves, raised their body, folded the rostrum towards the thorax and extended their ovipositor when selecting a site in which to oviposit. The ovipositor was inserted into the plant tissue by a downward and forward thrust of the body and contractions of the abdominal muscles. After a period of immobility, the ovipositor was retracted and the insect's body and organs returned to their initial positions. This behaviour was preceded and followed by extensive rostral exploration of the oviposition site. In most females the same area was explored before and after egg-laying and the ovipositor was inserted approximately in the middle of the selected area. The sequence and pattern of ovipositional behaviour varied between females.

Descriptions are given of the collection and rearing of Psychodopygus lainsoni Fraiha & Ward and five sympatric species, P. carrerai (Barretto), a member of the P. squamiventris group, Lutzomyia anduzei (Rozeboom) and two undescribed species closely related to L. anduzei (Rozeboom) designated L. sp. no. 260.43 and 260.44, all from the Altamira region of the Transamazônica highway, Pará State, Brazil. Fungal contamination of rearing containers and a reluctance of reared flies to feed prevented the establishment of closed colonies of these silvatic species. Storage of P. lainsoni eggs at 15°C delayed hatching, and reduced hatch rates and larval viability. Pupal storage at 12°C failed to inhibit emergence. Diapause is reported in the egg stage of L. sp. 260.44.

Three benzyl-l,3-benzodioxoles and three benzylphenols were tested for their ability to sterilise Glossina morsitans morsitans Westw. following topical application in acetone. Two of the former compounds, 5-ethoxy-6- (4-methoxyphenylmethyl)-l,3-benzodioxole and 5-ethoxy-6-[l-(4-meth-oxyphenyl)ethyl]-l,3-benzodioxole, caused total sterility in females at a dose of 10 μg per fly, and remained effective even after one year's storage at 4°C. Dose-fecundity data indicate a reduction to 50% fecundity (ED50) was achieved with 2·5 μg of the former or 0·5 μg of the latter per fly. An ED90 of 8·5 μg and 2·5 μg, respectively, is indicated. The latter compound reduced the survival of treated females and males and surviving males were incapable of inseminating even though copulation appeared normal. The effects on female survival and fecundity, of feeding the compounds at 0·25 and 1·0% in blood, were variable, owing to their low solubility and variations in the size of blood-meals. The highest doses of the former compound led to ovarian atrophy in females, which can be described as an effect on fecundity. Lower doses induced sterility through egg death and atrophy after ovulation. The latter compound acted more rapidly than the former, preventing ovulation of the first mature oocyte in a higher proportion of flies. The activity of these compounds, which were derived by modification of plant materials, and are non-mutagenic, renders them likely candidates for evaluation as contact insecticides for Glossina in the field.

1. A series of exploratory experiments on the relationship between temperature and toxicity of DDT films to adults of Tribolium castaneum, and larvae of Plutella maculipennis, are described. The main conclusions with T. castaneum are:—

(a) When the insects are continuously kept on the film at different temperatures there is a higher kill at higher temperatures.

(b) When the insects are exposed to the film for about 24 hours at the same temperature and then kept away from it at different temperatures there is a higher kill at the lower temperature.

(c) When the insects are kept on the film at different temperatures for about 24 hours and then kept away from the film for reaction at the same temperature, there is a higher kill in those kept on the film at the higher temperature.

(a) and (b) above apply equally to larvae of P. maculipennis but (c) is reversed. The probable cause of this reversal appears to be the observed fact that at higher temperatures these larvae cover the film with much more silk thread and thus avoid contact to a greater extent than at lower temperatures.

2. A review of literature, in the light of the conclusions arrived at, indicate that many of the observations made upon the temperature-toxicity relationship can be accounted for by the following generalisations:—

(a) Insect resistance to poisons changes with temperature as do its other vital activities, increasing up to a critical degree and afterwards declining.

(b) The amount of poison reaching the site of action in unit time also varies with the temperature, generally but not always, increasing with its rise. Insect activity, especially locomotor and respiratory, may play an important part in these effects.

(c) The apparent effects of temperature on insecticidal action is the combination of these two factors, namely, resistance and pick-up.

Pregnant females of Glossina morsitans morsitans Westw. were offered choices of larviposition sites in the vicinity of various models and patterns. Ground-level surfaces of black, green, white or red were not attractive. Vertical surfaces did not attract a majority of flies, but 50% of those that settled on them gave birth in that region of the chamber. Shade cast by horizontal surfaces was attractive, but shade cast by vertical objects was not. Models with an enclosed space were attractive, but larviposition rarely occurred within the model, probably because flies do not readily enter cavities unless the temperature is very high. Among patterns presented at a distance, a simple unbroken area of black was more attractive than equivalent areas in the form of stripes, etc. No distinction was made between stripes presented vertically, horizontally and at an angle. Models representing logs or trees with rot holes were not attractive. Models with subterranean cavities, even a simple trench, were attractive. Loose sand was not more attractive than sand glued to a substrate, but there was an indication of a preference for larger particles. No evidence was obtained for the hypothesis of Nash et al. (1976) that a larval pheromone attracts gravid females to larviposition sites.

Trials in East Africa (chiefly in Tanganyika) are described to show that the time taken for first-instar larvae of Busseola fusca (Fuller) to reach the more closely packed young leaves in the central axis of the maize plant is about ten days, and that insecticides are effective up to the end of this period. Results show that the best time for control is as near hatching of the eggs as possible, but with more persistent insecticides such as endrin, economic control is possible up to five days later.

A method of testing insecticides as residual deposits, by allowing first-instar larvae to walk on them, is given, and it was found that isodrin, DDT, endrin and γ BHC are highly effective as residual films. The MLD's for one minute in contact are 1·8 mg./sq.m. for isodrin, 4–7 mg. for DDT, 8·3 mg. for endrin and about 20 mg. for γ BHC. Derris emulsion has no residual effect after drying and is only effective in the liquid state after contact with larvae for several minutes.

In a series of field trials over three years, increases in yield of up to 2·6 times the control yields were shown to be possible, and averaged twice the control yield. Endrin was the most consistently effective insecticide, applied as a 2 per cent, dust and as a 0·03–0·04 per cent, emulsion spray. Two applications of endrin at an interval of two weeks were effective, but, for DDT, three applications of an emulsion containing 0·05 per cent. DDT at nine-day intervals were more effective than two while one may be of little value. An application of 2·5 oz./acre of DDT can be effective for 7–10 days, while 1·5 oz./acre of endrin can be effective for 14 days. In general, however, rates per application should not fall below 3·5 oz. DDT or 2 oz. endrin per acre, overall.

The superiority of a 5 per cent. DDT dust over one of 2·5 or 1 per cent, makes it more economical in a high-yielding, heavily attacked area. Diazinon and malathion in emulsion sprays are less persistent than DDT.

Trials with 4 per cent, malathion dust and 0·15 per cent, malathion emulsion spray were inconclusive on account of heavy damage by Spodoptera sp.

Attempts to increase the persistence of malathion and γ BHC by the addition of chlorinated terphenyl resins were also inconclusive, but DDT in emulsion, with resin, appeared more effective than DDT alone.

The economics of successful control measures at the prices obtaining at the time are discussed under the various trials.

Chemical estimations of the deposits of insecticides retained on the plants showed that between 1·4 and 3·7 per cent, of the quantity applied per unit area can be recovered in this way.

In a discussion of the significance of the results in control, it is suggested that spraying the stems only is half as effective as spraying the whole plant.

The conditions and results relating to two aerial spray trials are given.

The place of control of Busseola in agricultural practice is described, and some of the present results are quoted to show that yields can be increased by good farming practice as much as by control of Busseola.

1. When spring migrants of Aphis fabae, Scop., from Euonymus europaeus and Viburnum opulus are given a choice of summer host plants enclosed by a muslin cage, they colonise bean first and then sugar beet. Dock, poppy and Chenopodium are colonised in no very definite order, but thistle is the last plant to be infested.

2. Further infestation of surrounding plants takes place rapidly by means of apterae, which migrate actively and colonise plants at random.

3. The total number of Aphids on the summer host plants is of the same order as the times of colonisation.

4. The effect of parasites and predators is proportional to the numbers present and to the size of the colony.

5. The results do not indicate the presence of biological races on the chosen host plants.

I should like to thank Mr. F. G. W. Jones, of the School of Agriculture, Cambridge, for his help in preparing the ground for the plots and in rearing some of the plants, and Dr. W. H. Thorpe for his criticism.

In Trinidad, the only serious pod borer attacking pigeon peas is Ancylostomia stercorea (Zell.). This species breeds throughout the year. The eggs are laid on the young pods and the larvae feed on the developing seeds and later pupate in the soil. The complete life-cycle requires 26–32 days.

Eight species of parasites were reared from the larvae of Ancylostomia. Life-history studies and rearing techniques for the six commonest species are presented.

Apantelcs etiellae isolatus Mues. is a solitary endoparasite attacking first- to third-stage host larvae. It emerges from the fourth-stage host and constructs a white cocoon in the pod. The life-cycle takes 14–18 days.

Phanerotoma bennetti Mues. is a solitary egg-larval parasite. The egg is laid in that of the host, but the parasite does not complete development until the host has reached the final larval stage and constructed a cocoon. A generation is completed in 20 to 28 days. A method of breeding this species on Ephestia cautella (Wlk.) is described.

Eiphosoma annulatum Cress, is a solitary endoparasite attacking first- to fourth-stage hosts. The parasites emerge from fifth-stage hosts which may be stunted in size but construct normal cocoons. The life-cycle is completed in 26–35 days.

Bracon thurberiphagae (Mues.) and Bracon cajani Mues. are gregarious ectoparasites of similar habit. They paralyse second- to fifth-stage larvae and deposit eggs on or near them. The life-cycle is completed in 13 to 16 days. A method of rearing field-collected immature stages is described.

Perisierola sp. is a gregarious ectoparasite. The adult enters the pod, paralyses a host, and attaches her eggs directly on to the caterpillar. Second- to fifth-stage hosts may be attacked but the larger hosts are preferred. The female frequently remains with her progeny until they have completed their development, which requires 11 to 15-days.

Hyperparasites attacking the parasite pupae are listed.

Details of a shipping container and methods of rearing and shipping parasites to Mauritius for trial against Etiella zinckenella (Treitschke) and Maruca testulalis (Geyer) are described. From a stock of more than 44,000 cocoons so sent two species, Bracon cajani and Eiphosoma annulatum, have been successfully established in Mauritius.

The seasonal dynamics of neutral genetic diversity and the insecticide resistance mechanisms of insect pests at the farm scale are still poorly documented. Here this was addressed in the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) in Central Chile. Samples were collected from an insecticide sprayed peach (Prunus persica L.) orchard (primary host), and a sweet-pepper (Capsicum annum var. grossum L.) field (secondary host). In addition, aphids from weeds (secondary hosts) growing among these crops were also sampled. Many unique multilocus genotypes were found on peach trees, while secondary hosts were colonized mostly by the six most common genotypes, which were predominantly sensitive to insecticides. In both fields, a small but significant genetic differentiation was found between aphids on the crops vs. their weeds. Within-season comparisons showed genetic differentiation between early and late season samples from peach, as well as for weeds in the peach orchard. The knock-down resistance (kdr) mutation was detected mostly in the heterozygote state, often associated with modified acetylcholinesterase throughout the season for both crops. This mutation was found in high frequency, mainly in the peach orchard. The super-kdr mutation was found in very low frequencies in both crops. This study provides farm-scale evidence that the aphid M. persicae can be composed of slightly different genetic groups between contiguous populations of primary and secondary hosts exhibiting different dynamics of insecticide resistance through the growing season.